Multi-antenna GNSS control system and method

ABSTRACT

A global navigation satellite sensor system (GNSS) and gyroscope control system for vehicle steering control comprising a GNSS receiver and antennas at a fixed spacing to determine a vehicle position, velocity and at least one of a heading angle, a pitch angle and a roll angle based on carrier phase position differences. A vehicle control method includes the steps of computing a position and a heading for the vehicle using GNSS positioning and a rate gyro for determining vehicle attitude, which is used for generating a steering command.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims the benefit of:U.S. patent application Ser. No. 12/355,776, filed Jan. 17, 2009 nowU.S. Pat. No. 8,140,223, which is a continuation-in-part of Ser. No.12/171,399, filed Jul. 11, 2008 now U.S. Pat. No. 8,265,826, which is acontinuation-in-part of No. 10/804,758, filed Mar. 19, 2004, now U.S.Pat. No. 7,400,956; Ser. No. 10/828,745, filed Apr. 21, 2004; and U.S.Provisional Patent Applications No. 60/456,146, filed Mar. 20, 2003 andNo. 60/464,756, filed Apr. 23, 2003. The contents of all of theaforementioned applications are incorporated by reference herein intheir entireties.

BACKGROUND OF THE INVENTION

Movable machinery, such as agricultural equipment, open-pit miningmachines, airplane crop dusters and the like all benefit from accurateglobal navigation satellite system (GNSS) high precision surveyproducts, and others. However, in existing satellite positioning systems(SATPS) for guided parallel and contour swathing for precision farming,mining, and the like, the actual curvature of terrain may not be takeninto account. This results in a less than precise production because ofthe less than precise parallel or contour swathing. Indeed, in order toprovide swaths through a field (in farming, for example), the guidancesystem collects positions of the vehicle as it moves across the field.When the vehicle commences the next pass through the field, the guidancesystem offsets the collected positions for the previous pass by thewidth of the equipment (i.e. swath width). The next set of swathpositions is used to provide guidance to the operator as he or shedrives the vehicle through the field.

The current vehicle location, as compared to the desired swath location,is provided to the vehicle's operator or to a vehicle's steering system.The SATPS provides the 3-D location of signal reception (for instance,the 3-D location of the antenna). If only 3-D coordinates are collected,the next swath computations assume a flat terrain offset. However, theposition of interest is often not the same as where the satellitereceiver (SR) is located since the SR is placed in the location for goodsignal reception, for example, for a tractor towing an implement, anoptimal location for the SR may be on top of the cab. However, theposition of interest (POI) for providing guidance to the tractoroperator may be the position on the ground below the operator. If thetractor is on flat terrain, determining this POI is a simple adjustmentto account for the antenna height.

However, if the tractor is on an inclined terrain with a variable tilt,which is often the case, the SATPS alone cannot determine the terraintilt so the POI also cannot be determined. This results in a guidanceerror because the POI is approximated by the point of reception (POR),and this approximation worsens as the terrain inclination increases.This results in cross track position excursions relative to the vehicleground track which would contaminate any attempt to guide to a definedfield line or swath. On inclined terrain, this error can be minimized bycollecting the vehicle tilt configuration along each current pass or theprevious pass. The swath offset thus becomes a vector taking the terraininclination into account with the assumption that from the first swathto the next one the terrain inclination does not change too much. It cantherefore be seen that there is a need for a better navigation/guidancesystem for use with a ground-based vehicle that measures and takes intoaccount vehicle tilt.

Various navigation systems for ground-based vehicles have been employedbut each includes particular disadvantages. Systems using Doppler radarwill encounter errors with the radar and latency. Similarly, gyroscopes,which may provide heading, roll, or pitch measurements, may be deployedas part of an inertial navigation package, but tend to encounter drifterrors and biases and still require some external attitude measurementsfor gyroscope initialization and drift compensation. Gyroscopes havegood short-term characteristics but undesirable long-termcharacteristics, especially those gyroscopes of lower cost such as thosebased on a vibrating resonator. Similarly, inertial systems employinggyroscopes and accelerometers have good short-term characteristics butalso suffer from drift. Various systems include navigating utilizingGNSS; however, these systems also exhibit disadvantages. Existing GNSSposition computations may include lag times, which may be especiallytroublesome when, for example, GNSS velocity is used to derive vehicleheading. As a result, the position (or heading) solution provided by aGNSS receiver tells a user where the vehicle was a moment ago, but notin real time. Existing GNSS systems do not provide high quality headinginformation at slower vehicle speeds. Therefore, what is needed is a lowcost sensor system to facilitate vehicle swath navigation that makes useof the desirable behavior of both GNSS and inertial units whileeliminating or reducing non-desirable behavior. Specifically, what isneeded is a means to employ low-cost gyroscopes (e.g., microelectromechanical (MEM) gyroscopes) which exhibit very good short-termlow noise and high accuracy while removing their inherent long-termdrift.

Providing multiple antennas on a vehicle can provide additional benefitsby determining an attitude of the vehicle from the GNSS ranging signalsreceived by its antennas, which are constrained on the vehicle at apredetermined spacing. For example, high dynamic roll compensationsignals can be output directly to the vehicle steering usingGNSS-derived attitude information. Components such as gyroscopes andaccelerometers can be eliminated using such techniques. Real-timekinematic (RTK) can be accomplished using relatively economical singlefrequency L1—only receivers with inputs from at least two antennasmounted in fixed relation on a rover vehicle. Still further, movingbaselines can be provided for positioning solutions involving tractorsand implements and multi-vehicle GNSS control can be provided.

Providing additional antennas in combination with standard SATPS andGNSS guidance, as mentioned above, along with optional gyroscopes is agreat method to increase GNSS positioning precision and accuracy, suchas is described in U.S. Patent Publication No. 2009/0164067 which isassigned to a common assignee and is incorporated herein. However,accuracy and precision can only improve the efficiency of workingvehicles, such as those in the agricultural field, to a limited extent.Although such systems are able to track and guide vehicles in threedimensions, including along ridges and sloped-regions, errors may appearin other aspects of a working vehicle. For example, in an agriculturalfield-working situation where a tractor is towing an implement, theimplement may slide on a sloped-region, or the tractor may list to oneside or another when entering softer soil or rocky areas. This canhappen repeatedly when a vehicle is guided around the same field,regardless of the precision of the guidance system in pre-planning apath. Thus, a system that can detect such changes in uniformity of afield as the vehicle traverses a path and remember those changes canpredict and re-route a more accurate and more economical path than aguidance system alone. Heretofore there has not been available a systemand method with the advantages and features of the present invention.

SUMMARY OF THE INVENTION

Disclosed herein in an exemplary embodiment is a sensor system forvehicle steering control comprising: a plurality of global navigationsatellite systems (GNSS) including receivers and antennas at a fixedspacing to determine a vehicle position, velocity and at least one of aheading angle, a pitch angle and a roll angle based on carrier phasecorrected real time kinematic (RTK) position differences. The roll anglefacilitates correction of the lateral motion induced position errorsresultant from motion of the antennae as the vehicle moves based on anoffset to ground and the roll angle. The system also includes a controlsystem configured to receive the vehicle position, heading, and at leastone of roll, pitch and yaw, and configured to generate a steeringcommand to a vehicle steering system.

Also disclosed herein in another exemplary embodiment is a method forcomputing a position of a vehicle comprising: initializing GNSS;computing a first position of a first GNSS antenna on the vehicle;computing a second position of a second GNSS antenna; and calculating aheading as a vector perpendicular to a vector joining the first positionand the second position, in a horizontal plane aligned with the vehicle.The method also includes computing a roll angle of the vehicle as anarc-tangent of a ratio of differences in heights of the first GNSSantenna and the second GNSS antenna divided by a spacing between theirrespective phase centers and calculating an actual position at thecenter of the vehicle projected to the ground using the computed rollangle and a known height from the ground of at least one of the firstGNSS antenna and the second GNSS antenna.

Further disclosed herein in yet another exemplary embodiment is a methodof controlling a vehicle comprising: computing a position and a headingfor the vehicle; computing a steering control command based on aproportionality factor multiplied by a difference in a desired positionversus an actual position, plus a second proportionality factormultiplied by a difference in a desired heading versus an actualheading, the second proportionality factor ensuring that when thevehicle attains the desired position the vehicle is also directed to thedesired heading, and thereby avoiding crossing a desired track. Themethod also includes a recursive adaptive algorithm employed tocharacterize the vehicle response and selected dynamic characteristics.

The method further includes applying selected control values to avehicle steering control mechanism and measuring responses of thevehicle thereto; calculating response times and characteristics for thevehicle based on the responses; and calibrating the control commands byapplying a modified control command based on the responses to achieve adesired response. Various alternative aspects and applications of thepresent invention are disclosed herein.

Additional alternative aspects include selective sprayer nozzle control,high dynamic roll compensation using GNSS attitude solutions frommultiple antennas, moving baseline implement positioning and multiplevehicle control.

An additional exemplary embodiment is a sensor system for vehicleguidance using one or more global navigation satellite systems (GNSSs)according to the above-mentioned embodiments, in combination with aplurality of various sensors located throughout a vehicle and a towedimplement. These sensors detect additional parameters from thosecalculated by the GNSS positioning system, such as vehicle and implementstress levels, fuel levels, power levels, optical guide pathobservations via an onboard camera, multi-section (articulated)implement position and attitude sensing via multiple antennas and othercharacteristics of the working vehicle. The combination of the twosystems results in a much more accurate and economical preplanned pathgenerated for use in later field work.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an illustrative diagram of a vehicle including anexemplary embodiment;

FIG. 2 depicts an illustrative block diagram of the vehicle including anexemplary embodiment of a sensor system;

FIG. 3 depicts an illustrative block diagram of a sensor system inaccordance with an exemplary embodiment;

FIG. 4 depicts an illustrative sensor system in accordance with anexemplary embodiment;

FIG. 5 depicts an illustrative flow chart of an exemplary process fordetermining a steering command for a vehicle in accordance with anexemplary embodiment;

FIG. 6 depicts an illustrative flow chart of an exemplary process fordetermining a steering command with an exemplary sensor system inaccordance with an alternative embodiment;

FIG. 7A depicts a multi-axis antenna and gyroscope system embodying anaspect of the present invention and including two antennas connected bya rigid link and yaw and roll gyroscopes;

FIG. 7B depicts the system in a yaw attitude;

FIG. 7C depicts the system in a roll attitude;

FIG. 8 depicts a tilt (roll) angle measuring application of theinvention on an agricultural vehicle;

FIG. 9 depicts an alternative aspect of the system with antenna andgyroscope subsystems mounted on both the vehicle and the implement, e.g.a sprayer with selectively controllable spray nozzles;

FIG. 10 depicts a block diagram of the system shown in FIG. 9;

FIG. 11 depicts a high dynamic roll compensation GNSS guidance systemcomprising an alternative aspect of the present invention;

FIG. 12 depicts a block diagram of the system shown in FIG. 11;

FIG. 13 depicts an alternative aspect of the present inventioncomprising a moving baseline GNSS system with the tractor and theimplement each mounting a respective antenna for a 1+1 antennaconfiguration;

FIG. 14 depicts an enlarged, fragmentary view thereof, particularlyshowing implement yaw and pitch movements in connection with the movingantenna-to-antenna baseline.

FIG. 15 depicts another moving baseline alternative aspect in a 2+1antenna configuration.

FIG. 16 depicts another moving baseline alternative aspect in a 2+2antenna configuration.

FIG. 17 depicts the 2+1 moving baseline system in a contour mode ofoperation with a multi-position tail;

FIG. 18 depicts a block diagram of the moving baseline system(s);

FIG. 19 depicts a multi-vehicle GNSS relative guidance system includingprimary and secondary rovers; and

FIG. 20 depicts a block diagram of the system shown in FIG. 19.

FIG. 21 depicts an upper, front, right-side isometric view of a vehicleequipped with a GNSS-based control system comprising another alternativeembodiment of the present invention, and also depicts X, Y and Z axescorresponding to roll, pitch and yaw rotation respectively of thevehicle.

FIG. 22 depicts an isometric view of the vehicle and a block diagram ofthe control system components.

FIG. 23A depicts an isometric view showing the relative locations of atractor-mounted antenna and two implement-mounted antennas thereof, withthe implement directly in line behind the tractor.

FIG. 23B depicts an isometric view thereof showing the relativelocations of the antennas with the implement swung to the left behindthe tractor.

FIG. 23C is a right side elevational view thereof depicting the relativelocations of the tractor antenna and an implement antenna.

FIG. 24 depicts a block diagram of the guidance system.

FIG. 25 depicts a block diagram of the flow of data among the variousvehicle control system components.

FIG. 26 depicts the system controlling a tractor towing an implement ina cultivated field.

FIG. 27 is a flowchart of a method of the present invention.

FIG. 28 is a perspective view of a guidance system on an agriculturalvehicle comprising another alternative aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED ASPECTS I. GNSS Introduction

Global navigation satellite systems (GNSS) are broadly defined toinclude GPS (U.S.), Galileo (proposed), GLONASS (Russia), Beidou/Compass(China, proposed), IRNSS (India, proposed), QZSS (Japan, proposed) andother current and future positioning technology using signals fromsatellites, with or without augmentation from terrestrial sources.Inertial navigation systems (INS) include gyroscopic (gyro) sensors,accelerometers and similar technologies for providing outputcorresponding to the inertia of moving components in all axes, i.e.through six degrees of freedom (positive and negative directions alongtransverse X, longitudinal Y and vertical Z axes). Yaw, pitch and rollrefer to moving component rotation about the Z, X and Y axesrespectively. Said terminology will include the words specificallymentioned, derivatives thereof and words of similar meaning.

Disclosed herein in an exemplary embodiment is a sensor system forvehicle guidance. The sensor system utilizes a plurality of GNSS carrierphase differenced antennas to derive attitude information, hereinreferred to as a GNSS attitude system. Moreover, the GNSS attitudesystem may optionally be combined with one or more rate gyro(s) used tomeasure turn, roll or pitch rates and to further calibrate bias andscale factor errors within these gyros. In an exemplary embodiment, therate gyros and GNSS receiver/antenna are integrated together within thesame unit, to provide multiple mechanisms to characterize a vehicle'smotion and position to make a robust vehicle steering control mechanism.

It is known in the art that by using a GNSS satellite's carrier phase,and possibly carrier phases from other satellites, such as WAASsatellites, a position may readily be determined to within millimeters.When accomplished with two antennas at a fixed spacing, an angularrotation may be computed using the position differences. In an exemplaryembodiment, two antennas placed in the horizontal plane may be employedto compute a heading (rotation about a vertical Z axis) from a positiondisplacement. It will be appreciated that an exemplary embodiment may beutilized to compute not only heading, but either roll (rotation about alongitudinal Y axis) or pitch (rotation about a lateral X axis)depending on the orientation of the antennas relative to the vehicle.Heading information, combined with position, either differentiallycorrected (DGPS or DGNSS) or carrier phase corrected real time kinematic(RTK) provides the feedback information desired for a proper control ofthe vehicle direction. Addition of one or more rate gyros furtherprovides independent measurements of the vehicle's dynamics andfacilitates vehicle steering control. The combination of GNSS attitudeobtained from multiple antennas with gyroscopes facilitates calibrationof gyroscope scale factor and bias errors which are present in low costgyroscopes. When these errors are removed, gyro rates are more accurateand provide better inputs for guidance and control. Furthermore,gyroscopes can now effectively be integrated to obtain roll, pitch andheading angles with occasional adjustment from the GNSS-derivedattitude.

Existing systems for vehicle guidance may employ separate gyros, andseparate GNSS positioning or attitude systems. However, such systems donot provide an integrated heading sensor based on GNSS as disclosedherein. Moreover, separate systems exhibit the limitations of theirrespective technologies as mentioned earlier. The exemplary embodimentsas described herein eliminate the requirements of existing systems forother means to correct for vehicle roll. Moreover, an implementation ofan exemplary embodiment also provides a relatively precise, in both thesort-term and the long-term, means of calculating heading and headingrate of change (turn rate).

Another benefit achieved by incorporating a GNSS-based heading sensor isthe elimination or reduction of drift and biases resultant from agyro-only or other inertial sensor approach. Yet another advantage isthat heading may be computed while the vehicle is stopped or movingslowly, which is not possible in a single-antenna GNSS based approachthat requires a vehicle velocity vector to derive heading. This can bevery important in applications where a vehicle has to turn slowly toalign with another path. During these slow turns the gyro can drift awaybut by adding the use of a dual antenna GNSS solution the orientation ofthe gyro can be continuously corrected. This also permits immediateoperation of a slow moving vehicle after being at rest, rather thanrequiring an initialization from motion. Yet another advantage of anexemplary embodiment is that a combination of the aforementioned sensorsprovides sufficient information for a feedback control system to bedeveloped, which is standalone and independent of a vehicle's sensors oradditional external sensors. Thus, such a system is readily maintainedas vehicle-independent and may be moved from one vehicle to another withminimal effort. Yet another exemplary embodiment of the sensor employsglobal navigation satellite system (GNSS) sensors and measurements toprovide accurate, reliable positioning information. GNSS sensorsinclude, but are not limited to GNSS, Global Navigation System (GLONAS),Wide Area Augmentation System (WAAS) and the like, as well ascombinations including at least one of the foregoing.

An example of a GNSS is the Global Positioning System (GPS) establishedby the United States government that employs a constellation of 24 ormore satellites in well-defined orbits at an altitude of approximately26,500 km, These satellites continually transmit microwave L-band radiosignals in two frequency bands, centered at 1575.42 MHz and 1227.6 MHz.,denoted as L1 and L2 respectively. These signals include timing patternsrelative to the satellite's onboard precision clock (which is keptsynchronized by a ground station) as well as a navigation message givingthe precise orbital positions of the satellites, an ionosphere model andother useful information. GNSS receivers process the radio signals,computing ranges to the GNSS satellites, and by triangulating theseranges, the GNSS receiver determines its position and its internal clockerror.

In standalone GNSS systems that determine a receiver's antenna positioncoordinates without reference to a nearby reference receiver, theprocess of position determination is subject to errors from a number ofsources. These include errors in the GNSS satellite's clock reference,the location of the orbiting satellite, ionosphere induced propagationdelay errors, and troposphere refraction errors.

To overcome the errors of the standalone GNSS system, many positioningapplications have made use of data from multiple GNSS receivers.Typically, in such applications, a reference receiver, located at areference site having known coordinates, receives the GNSS satellitesignals simultaneously with the receipt of signals by a remote receiver.Depending on the separation distance between the two GNSS receivers,many of the errors mentioned above will affect the satellite signalsequally for the two receivers. By taking the difference between signalsreceived both at the reference site and the remote location, the errorsare effectively eliminated. This facilitates an accurate determinationof the remote receiver's coordinates relative to the referencereceiver's coordinates.

The technique of differencing signals from two or more GNSS receivers toimprove accuracy is known as differential GNSS (DGNSS or DGPS).Differential GNSS is well known and exhibits many forms. In all forms ofDGNSS, the positions obtained by the end user's remote receiver arerelative to the position(s) of the reference receiver(s). GNSSapplications have been improved and enhanced by employing a broaderarray of satellites such as GNSS and WAAS. For example, see commonlyassigned U.S. Pat. No. 6,469,663 B1 to Whitehead et al. titled Methodand System for GNSS and WAAS Carrier Phase Measurements for RelativePositioning, dated Oct. 22, 2002, the disclosures of which areincorporated by reference herein in their entirety. Additionally,multiple receiver DGNSS has been enhanced by utilizing a single receiverto perform differential corrections. For example, see commonly assignedU.S. Pat. No. 6,397,147 B1 to Whitehead titled Relative GNSS PositioningUsing a Single GNSS Receiver with Internally Generated DifferentialCorrection Terms, dated May 28, 2002, the disclosures of which areincorporated by reference herein in their entirety.

II. GNSS and Gyro Control System and Method

Referring now to FIGS. 1 through 4, an illustrative vehicle 10 isdepicted including a sensor system 20 in accordance with an exemplaryembodiment. Referring also to FIGS. 2 and 3, block diagrams of thesensor system 20 are depicted. The sensor system 20 includes, but is notlimited to a GNSS attitude system 22, comprising at least a GNSSreceiver 24 and an antenna 26. The GNSS receiver/antenna systemscomprising GNSS attitude system 22 cooperate as a primary receiversystem 22 a and a secondary receiver system 22 b, with their respectiveantennas 26 a and 26 b mounted with a known separation. The primaryreceiver system 22 a may also be denoted as a reference or masterreceiver system, while the secondary receiver system 22 b may also bedenoted as a remote or slave receiver system. It will also beappreciated that the selection of one receiver as primary versussecondary need not be of significance; it merely provides a means fordistinguishing between systems, partitioning of functionality, anddefining measurement references to facilitate description. It should beappreciated that the nomenclature could readily be transposed ormodified without impacting the scope of the disclosure or the claims.

The sensor system 20 is optionally configured to be mounted within asingle enclosure 28 to facilitate transportability. In an exemplaryembodiment, the enclosure 28 can be any rigid assembly, fixture, orstructure that causes the antennas 26 to be maintained in asubstantially fixed relative position with respect to one another. In anexemplary embodiment, the enclosure 28 may be a lightweight bracket orstructure to facilitate mounting of other components andtransportability. Although the enclosure 28 that constrains the relativelocation of the two antennas 26 a and 26 b may have virtually anyposition and orientation in space, the two respective receivers 24(reference receiver 24 a and remote receiver 24 b) are configured tofacilitate communication with one another and resolve the attitudeinformation from the phase center of the reference antenna 26 a to thephase center of the remote antenna 26 b with a high degree of accuracy.

Yet another embodiment employs a GNSS sensor 20 in the embodiments aboveaugmented with supplementary inertial sensors 30 such as accelerometers,gyroscopes, or an attitude heading reference system. More particularly,in an implementation of an exemplary embodiment, one or more rategyro(s) are integrated with the GNSS sensor 20.

In yet another exemplary embodiment, a gyro that measures roll-rate mayalso be combined with this system's GNSS-based roll determination. Aroll rate gyro denoted 30 b would provide improved short-term dynamicrate information to gain additional improvements when computing the swayof the vehicle 10, particularly when traveling over uneven terrain.

It will be appreciated that to supplement the embodiments disclosedherein, the data used by each GNSS receiver 24 may be coupled with datafrom supplementary sensors 50, including, but not limited to,accelerometers, gyroscopic sensors, compasses, magnetic sensors,inclinometers, and the like, as well as combinations including at leastone of the foregoing. Coupling GNSS data with measurement informationfrom supplementary sensors 30, and/or correction data for differentialcorrection improves positioning accuracy, improves initializationdurations and enhances the ability to recover for data outages.Moreover, such coupling may further improve, e.g., reduce, the length oftime required to solve for accurate attitude data.

It will be appreciated that although not a requirement, the location ofthe reference antenna 26 a can be considered a fixed distance from theremote antenna 26 b. This constraint may be applied to the azimuthdetermination processes in order to reduce the time required to solvefor accurate azimuth, even though both antennas 26 a and 26 b may bemoving in space or not at a known location. The technique of resolvingthe attitude information and position information for the vehicle 10 mayemploy carrier phase DGNSS techniques with a moving reference station.Additionally, the use of data from auxiliary dynamic sensors aids thedevelopment of a heading solution by applying other constraints,including a rough indication of antenna orientation relative to theEarth's gravity field and/or alignment to the Earth's magnetic field.

Producing an accurate attitude from the use of two or more GNSS receiverand antenna systems 22 has been established in the art and thereforewill not be expounded upon herein. The processing is utilized herein aspart of the process required to implement an exemplary embodiment.

Referring also to FIG. 4, a mechanism for ensuring an accurateorientation of the sensor system 20 to the vehicle 10 may be providedfor by an optional mounting base 14 accurately attached to the enclosure28. An accurate installation ensures that substantially no misalignmenterror is present that may otherwise cause the sensor system 20 toprovide erroneous heading information. The mounting base 14 isconfigured such that it fits securely with a determinable orientationrelative to the vehicle 10. In an exemplary embodiment, for example, themounting base 14 is configured to fit flatly against the top surfaces ofthe vehicle 10 to facilitate an unimpeded view to the GNSS satellites.

With the sensor system 20 affixed and secured in the vehicle 10 power upand initialization of the sensor system 20 is thereafter executed. Suchan initialization may include, but not be limited to, using the controlsystem 100 to perform any initialization or configuration that may benecessary for a particular installation, including the configuration ofan internal log file within the memory of the sensor system 20.

The sensor system 20 may further include additional associatedelectronics and hardware. For example, the sensor system 20 may alsoinclude a power source 32, e.g., battery, or other power generationmeans, e.g., photovoltaic cells, and ultrahigh capacity capacitors andthe like. Moreover, the sensor system 20 may further include a controlsystem 100. The control system 100 may include, without limitation, acontroller/computer 102, a display 104 and an input device 106, such asa keypad or keyboard for operation of the control system 100. Thecontroller 102 may include, without limitation, a computer or processor,logic, memory, storage, registers, timing, interrupts, input/outputsignal interfaces, and communication interfaces as required to performthe processing and operations prescribed herein. The controllerpreferably receives inputs from various systems and sensor elements ofthe sensor system 20 (GNSS, inertial, etc.), and generates outputsignals to control the same and direct the vehicle 10. For example, thecontroller 102 may receive such inputs as the GNSS satellite andreceiver data and status, inertial system data, and the like fromvarious sensors. In an exemplary embodiment, the control system 100computes and outputs a cross-track and/or a direction error relating tothe current orientation, attitude, and velocity of the vehicle 10 aswell as computing a desired swath on the ground. The control system 100will also allow the operator to configure the various settings of thesensor system 20 and monitor GNSS signal reception and any other sensorsof the sensor system 20. In an exemplary embodiment, the sensor system20 is self-contained. The control system 100, electronics, receivers 24,antennas 26, and any other sensors, including an optional power source,are contained within the enclosure 12 to facilitate ease ofmanipulation, transportability, and operation.

Referring now to FIG. 5, a flowchart diagrammatically depicting anexemplary methodology for executing a control process 200 is provided.An exemplary control process 200, such as may be executed by an operatorin conjunction with a control system 100, acts upon information from thesensor system 20 to output cross-track and/or direction error based uponcorrected 3-D position, velocity, heading, tilt, heading rate (degreesper second), radius of curvature and the like.

System 22 a computes its position, denoted p₁ (x₁, y₁, z₁). Referringnow to block 220, the secondary receiver and antenna system 22 bcomputes its position, denoted p₂ (x₂, y₂, z₂). Referring now to block230, optionally additional receiver and antenna system(s) 22 computetheir respective positions, denoted p₃ (x₃, y₃, z₃), . . . p_(n) (x_(n),y_(n), z_(n)).

At process block 240, employing a geometric calculation the heading iscomputed as the vector perpendicular to the vector joining the twopositions, in the horizontal plane (assuming they are aligned with thevehicle 10). Furthermore, at block 250 the roll of the vehicle 10 mayreadily be computed as the arc-tangent of the ratio of the difference inheights of the two antennas 26 a and 26 b divided by the spacing betweentheir phase centers (a selected distance within the enclosure 12). Itwill be appreciated that optionally, if additional receiver and antennasystems are utilized and configured for additional measurements, thepitch and roll angles may also be computed using differentialpositioning similar to the manner for computing heading. Therefore, inFIG. 5, optionally at process block 260, the pitch and roll may becomputed.

Continuing with FIG. 5, at process block 270, using the computed rollangle and a known antenna height (based on the installation in a givenvehicle 10), the actual position at the center of the vehicle 10projected to the ground may be calculated. This position represents atrue ground position of the vehicle 10. Once the ground position isknown, the error value representing the difference between where thevehicle should be based on a computed swath or track, and where itactually is, can be readily calculated as shown at block 280.

Optionally, the vector velocities of the vehicle 10 are also known orreadily computed based on an existing course and heading of the vehicle10. These vector velocities may readily be utilized for control andinstrumentation tasks.

Turning now to FIG. 6, in another exemplary embodiment a steeringcontrol process 300 can utilize the abovementioned information from thesensor system 20 to direct the vehicle motion. At process block 310 thesteering control may be initiated by obtaining the computed errors fromprocess 200. Turning to block 320, the steering control process 300 maybe facilitated by computing a steering control command based on aproportionality factor times the difference in desired position versusactual position (computed position error), plus a second proportionalityfactor times the difference in desired heading versus actual heading(heading error). The second proportionality factor ensures that when thevehicle attains the desired position it is actually directed to thecorrect heading, rather than crossing the track. Such an approach willdramatically improve steering response and stability. At process block330, a steering command is generated and directed to the vehicle 10.

Moreover, continuing with FIG. 6, optionally a recursive adaptivealgorithm may also be employed to characterize the vehicle response andselected dynamic characteristics. In an exemplary embodiment, the sensorsystem 20 applies selected control values to the vehicle steeringcontrol mechanism as depicted at optional block 340 and block 330. Thesensor system 20 measures the response of the vehicle 10 as depicted atprocess block 350 and calculates the response times and characteristicsfor the vehicle. For example, a selected command is applied and theproportionality of the turn is measured given the selected change insteering. Turning to process block 360, the responses of the vehicle 10are then utilized to calibrate the control commands applying a modifiedcontrol command to achieve a desired response. It will be appreciatedthat such an auto-calibration feature would possibly be limited byconstraints of the vehicle to avoid excess stress or damage as depictedat 370.

It will be appreciated that while a particular series of steps orprocedures is described as part of the abovementioned alignment process,no order of steps should necessarily be inferred from the order ofpresentation. For example, the process 200 includes installation andpower up or initialization. It should be evident that power-up andinitialization could potentially be performed and executed in advancewithout impacting the methodology disclosed herein or the scope of theclaims.

It should further be appreciated that while an exemplary partitioningfunctionality has been provided, it should be apparent to one skilled inthe art that the partitioning could be different. For example, thecontrol of the primary receiver 24 a and the secondary receiver 24 b, aswell as the functions of the controller 102, could be integrated inother units. The processes for determining the alignment may, for easeof implementation, be integrated into a single receiver. Suchconfiguration variances should be considered equivalent and within thescope of the disclosure and claims herein.

The disclosed invention may be embodied in the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. The present invention can also be embodied in the form ofcomputer program code containing instructions embodied in tangiblemedia, such as floppy diskettes, CD-ROMs, hard drives, or any othercomputer-readable storage medium 80 wherein the computer becomes anapparatus for practicing the invention when the computer program code isloaded into and executed by the computer. The present invention can alsobe embodied in the form of computer program code stored in a storagemedium or loaded into and/or executed by a computer, for example. Thepresent invention can also be embodied in the form of a data signal 82transmitted by a modulated or unmodulated carrier wave, over atransmission medium, such as electrical wiring or cabling, through fiberoptics or via electromagnetic radiation. When the computer program codeis loaded into and executed by a computer, the computer becomes anapparatus for practicing the invention. When implemented on ageneral-purpose microprocessor, the computer program code segmentsconfigure the microprocessor to create specific logic circuits.

III. Alternative Aspect GNSS Control Systems and Methods

FIG. 7A shows another alternative aspect of the invention including aGNSS antenna and gyroscope attitude system 402 with antennas 405, 406separated by a rigid link 407. In a typical application, the rigid link407 is attached to the vehicle 10 and extends along the X (transverse)axis or transversely with respect to the vehicle's direction of travel,which generally corresponds to the Y (heading) axis. Alternatively, thevehicle 10 itself can provide the rigid link between the antennas 405,406, for example, by mounting the antennas 405, 406 at predetermined,fixed locations on the roof of the vehicle cab with a predetermined,fixed distance therebetween. Another alternative is to provide a GNSSattitude device with antennas, receivers and sensors (e.g., gyroscopes(gyros), accelerometers and other sensors) in a self-contained, unitaryenclosure, such as the device 20 shown in enclosure 28 in FIG. 4.Regardless of the antenna-mounting structure, the orientation of theantenna pair and the rigid link 407 (or vehicle 10) is determined withrespect to an Earth-fixed coordinate system. The XYZ axes shown in FIG.7A provide an example for defining this relation. Roll and yaw gyros430, 440 are generally aligned with the Y and Z axes respectively fordetecting and measuring vehicle 10 attitude changes with respect tothese axes.

With the system 402 installed on a vehicle 10 (FIG. 8), the two antennas405, 406 can provide angular orientations with respect to two axes. Inthe example shown, angular orientation with respect to the Y (heading)axis corresponds to vehicle roll and with respect to the Z (vertical)axis corresponds to vehicle yaw. These orientations are commonly ofinterest in agricultural vehicles whereby this is the preferred mountingand orientation arrangement for such applications. The vehicle's rollmost adversely affects GNSS-measured vehicle cross-track error. Bymeasuring the vehicle's roll, such cross-track errors can be compensatedfor or eliminated. Such roll-induced cross-track errors include variableroll errors due to uneven terrain and constant roll errors due to hillslopes. It will be appreciated that adding a third antenna providesthree-axis (XYZ) attitude solutions corresponding to pitch, roll andyaw. Of course, reorienting the two-antenna system 402 can provide otherattitude solutions. For example, locating the antennas' baseline(aligned with the rigid link 407) fore-and-aft along the vehicle's Yaxis will provide pitch and yaw attitudes.

FIG. 7B shows the system 402 in a yaw attitude or condition whereby thevehicle 10 has deviated from a desired heading along the Y axis to anactual heading by a yaw angle θ_(Y). In other words, the vehicle 10 hasrotated (yawed) clockwise with respect to the Z axis. FIG. 7C shows thesystem 402 in a roll attitude or condition whereby the vehicle 10 hasdeviated from level to a tilt or roll angle of θ_(R). In other words,the vehicle 10 has rotated (rolled) counterclockwise with respect to theY axis.

The system 402 includes roll and yaw gyros 430, 440 mounted and orientedfor detecting vehicle rotational movement with respect to the Y and Zaxes. The system 402 represents a typical strap-down implementation withthe vehicle 10, antennas 405, 406 and gyros 430, 440 rigidly connectedand moving together. A body-fixed coordinate system is thus defined withthe three perpendicular axes XYZ.

In all but the most extreme farmlands, the vehicle 10 would normallydeviate relatively little from level and horizontal, usually less than30° in most agricultural operations. This simplifies the process ofcalibrating the gyros 430, 440 using the GNSS attitude system 402consisting of two or more antennas 405, 406. For simplicity, it isassumed that the body-fixed axes XYZ remain relatively close to level.Thus, the change in the heading (yaw) angle θ_(Y) of FIG. 7B isapproximately measured by the body-fixed yaw gyro 440, even though theremay be some small discrepancy between the axes of rotation. Similarassumptions can be made for the roll angle θ_(R) (FIG. 7C), which isapproximately measured by the body-fixed roll gyro 430. A similarassumption could be used for measuring pitch attitude or orientationangles with a pitch gyro.

This simplifying assumption allows the gyros to be decoupled from oneanother during integration and avoids the necessity of using a fullstrap-down quaternion implementation. For example, heading deviation isassigned only to the yaw gyro 440 (gyro axis perturbations from theassumed level axis alignment are ignored). Similarly, vehicle roll isassumed to be measured completely by a single roll gyro 430. GNSSattitude-measured heading and roll can then be used to calibrate thegyros 430, 440. Such simplifying assumptions tend to be relativelyeffective, particularly for agricultural operations on relatively flat,level terrain. Alternatively, a full six-degrees-of-freedom strap-downgyro implementation with quaternion integration could be employed, butsuch a solution would normally be excessive and represent an ineffectiveuse of computing resources, unless an inertial navigation system (INS)was also being used to backup GNSS, for example, in the event of GNSSsignal loss.

For the purpose of calibrating the gyroscopes 430, 440, the anglesmeasured by the GNSS attitude system 402 are used as truth in a Kalmanfilter estimator of gyro bias and scale factor errors. Over a smallinterval of time, T, the following equation holds:{dot over ( θ _(gyro) T=Aθ _(true) +BTWhere{dot over ( θ _(gyro)=average gyro reading over

$T = {{1/n}{\sum\limits_{n}{\overset{.}{\theta}}_{gyro}}}$(with n readings taken over time T)θ_(true)=truth angular change over interval T as measured by the GNSSattitude system.A=gyro scale factor errorB=gyro rate bias error

A two state Kalman filter is defined to have the gyro rate basis andscale factor error as states. The Kalman process model is a first-orderMarkov:

$X_{k + 1} = {{\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}X_{k}} + {\begin{bmatrix}\sigma_{A} & 0 \\0 & \sigma_{B}\end{bmatrix}W_{k}}}$where the state vector X=[A B]Here σ_(A) and σ_(B) are noise amplitudes and W is white noise. Thisdictates what is known as a random walk of the state [A B]. The designerof the Kalman filter chooses σ_(A) and σ_(B) according to how rapidlythe bias and scale factor errors are expected to vary (usuallyvariations due to temperature dependencies of scale and bias in a lowcost gyro). Typical variations, especially of the scale factor, arequite small (A and B are nearly constant), and σ_(A) and σ_(B) arechosen accordingly. Typical values for a low-cost gyroscope, using atime interval T are:

${\sigma_{A} = \frac{0.02T}{1200}},{\sigma_{B} = \frac{T}{1200}}$where T is expressed in seconds and 1200 means 1200 seconds. Forexample, here the random walk is chosen to cause a drift in scale factorof 0.02 in 1200 seconds. The Kalman measurement equation is:y=Hx+vWherey={dot over ( θ _(gyro)T, H=[θ_(true) T] and v is measurement noise. TheKalman covariance propagation and gain calculation is designed accordingto well-known techniques.

Similar Kalman filters are deployed in both yaw and roll (and/or pitch)channels. The GNSS attitude devices 20 provides a reference yaw and rollthat act as the Kalman measurements enabling the calibration of gyrorate basis and scale factor errors. The GNSS device provides heading androll, even when the vehicle is stationary or traveling in reverse. Thisprovides a significant advantage over single-antenna systems whichprovide a vehicle direction only when moving (i.e., a velocity vector).The multi-antenna attitude device 20 enables continuous calibrationregardless of whether or not and in what direction the vehicle 10 ismoving.

The calibrated gyros 430, 440 are highly advantageous in a vehiclesteering control system. High precision heading and heading-rateproduced by the calibrated yaw gyro is a very accurate and instantaneousfeedback to the control of vehicle changes in direction. The angularrate produced by the gyro is at least an order of magnitude moreaccurate than the angular rate produced by pure GNSS systems, even thosewith multiple antennas. The system 402 is also very responsive. Thefeedback control needs such relatively high accuracy and responsivenessin heading and heading-rate to maintain control loop stability. It iswell known that rate feedback in a control loop enhances stability. On afarm vehicle, where vehicle dynamics may not be fully known or modeled,this aspect is particularly important. The rate term allows a genericcontrol system to be developed which is fairly insensitive to un-modeledvehicle dynamics. A relatively accurate heading and heading-rate-of-turncan be calculated for use in a vehicle automatic steering system.

Another advantage of the system 402 is that a gyro calibrated to measuretilt angle can provide the vehicle's tilt much more accurately than asystem relying exclusively on GNSS positioning signals. This advantageis particularly important in high-precision autosteering, e.g., to thecentimeter level. Errors in GNSS attitude are effectively increased bythe ratio of the antenna spacing to the mounted height of the antennasabove the ground, as illustrated in FIG. 8, which shows an attitudesystem 402 comprising a pair of antennas 405, 406 connected by a link407, as described above. The system 402 is shown tilted through a tilt(roll) angle θ_(R). An imaginary antenna height line perpendicular tothe rigid link 407 is projected to the “true” ground position of thevehicle 10 in FIG. 8 and forms the roll angle with respect to the Zaxis. The relative antenna height differential can be projected alongthe vertical Z axis to a ground intercept point and establishes across-track error (distance between the vehicle true ground position andthe Z axis ground intercept point), whereby errors in the antenna heightdifferential are amplified by the ratio of the rigid link 407 length tothe antenna height. The spacing of the antennas 405, 406, whichcorresponds to the length of the rigid link 407, is typically limited bythe width of the vehicle 10, which can be relatively tall, therebyresulting in a relatively large antenna height-to-spacing ratio, e.g.,five-to-one. Furthermore, noise-induced errors present in GNSS relativeantenna height differentials (e.g., carrier phase noise, etc.) will bemultiplied by this ratio, which can cause steering errors, includingsteering oscillations, etc.

The GNSS attitude system 402 utilizes a roll gyro (e.g., 430) formeasuring rate-of-change of the roll angle, rather than the absoluteroll angle, which rate of change is integrated to compute absolute rollangle. The constant of integration can be initialized to the currentGNSS-derived roll angle and then subsequently steered to the GNSS rollangle by filtering with a Hatch filter or similar filter used forsmoothing the code phase against the carrier phase in the GNSSreceivers. Relatively smooth vehicle roll estimates can thus be achievedwith a gyro.

More specifically, in an exemplary embodiment, the filtering issupplemented by the equation:θ_(filter)(k)=Δ_(gyro)(k)+Gain*[θ_(GNSS)(k)−θ_(filter)(k−1)−Δ_(gyro)(k)]Δ_(gyro)(k)=θ_(gyro)(k)−θ_(gyro)(k−1)Where θ_(filter)(k) is the desired output roll angle (at time k)smoothed by gyro roll angle, but steered to GNSS roll angle. The GNSSroll (at time k) is θ_(GNSS)(k) while the raw gyro angular reading isθ_(gyro)(k) which is obtained by integrating gyro angular rate. Thedifference in gyro integrated rate over one time interval (k−1 to k) isdenoted Δ_(gyro)(k). The filter bandwidth and weighting of the GNSS rollangle into the solution is set by the filter's gain (denoted Gain). Onemethod to choose the gain is to assign Gain=T/τ where T is the time spanfrom epoch to epoch and τ is a time-constant, typically much larger thanT. The smaller the Gain, the less the GNSS roll angle is weighted intothe solution. The gain is chosen to give a smooth filtered roll output,dominated by the low gyro noise characteristics, but also maintainingalignment with GNSS roll. Since the gyro is calibrated in terms of itsscale and bias errors per the methods described earlier, the gain can bechosen to be very small (much less than 1) and still the filtered rollangle closely follows the GNSS roll angle, but without the noise of theGNSS derived roll angle. Similar schemes can be deployed for pitch andheading angles if needed, all with the benefit of improved steering ifsuch angles are used in the steering control feedback.

FIG. 9 shows a GNSS and gyroscopic control system 502 comprising analternative aspect of the present invention in a tractor and sprayeragricultural equipment application 504. The vehicle (e.g., a motivecomponent or tractor) 10 is connected to a working component (e.g., asprayer) 506 by an articulated connection 508, which can comprise aconventional tongue-and-hitch connection, or a powered, implementsteering system or hitch, such as those shown in U.S. Pat. No.6,865,465, No. 7,162,348 and No. 7,373,231, which are assigned to acommon assignee herewith and are incorporated herein by reference.

The tractor 10 and the sprayer 506 mount tractor and sprayer GNSSantenna and gyroscope attitude subsystems 510, 512 respectively, whichare similar to the system 402 described above and provide GNSS-derivedposition and attitude outputs, supplemented by gyro-derived rate ofrotation outputs for integration by the control system 502. The sprayer506 includes a spray boom 514 with multiple nozzles 516 providing spraypatterns 518 as shown, which effectively cover a swath 520. The system502 can be programmed for selectively controlling the nozzles 516. Forexample, a no-spray area 522 is shown in FIG. 9 and can comprise, forexample, an area previously sprayed or an area requiring spray. Based onthe location of the no-spray area 522 in relation to the spray boom 514,one or more of the nozzles 516 can be selectively turned on/off.Alternatively, selective controls can be provided for other equipment,such as agricultural planters wherein the seed boxes can be selectivelyturned on/off.

FIG. 10 shows some of the major components of the system 502, includingthe GNSS antenna and gyroscope attitude subsystems 510, 512 withantennas 405, 406 separated by rigid links 407, as described above, andinertial gyros 514. The tractor and implement 10, 506 can be equippedwith comparable systems including DGNSS receivers 524, suitablemicroprocessors 526 and the inertial gyros 529. Additional sensors 528can include wheel counters, wheel turn sensors, accelerometers, etc. Thesystem components can be interconnected by a CAN connection 530.Alternatively, components can be wirelessly interconnected, e.g., withRF transmitters and receivers.

In operation, the functions described above can be implemented with thesystem 502, which has the additional advantage of providing GNSS andgyro-derived positioning and attitude signals independently from thetractor 10 and the implement 506. Such signals can be integrated by oneor both of the microprocessors 526. The tractor 10 can be automaticallysteered accordingly whereby the implement 506 is maintained on course,with the additional feature of selective, automatic control of thenozzles 516. For example, FIG. 9 shows the course of the tractor 10slightly offset to the course of the sprayer 516, which condition couldbe caused by a downward left-to-right field slope. Such sloping fieldconditions generate roll attitudes, which could also be compensated foras described above. For example, the system 502 can adjust the outputfrom the spray nozzles 516 to compensate for such variable operatingconditions as sloping terrain, turning rates, tire slippage, systemresponsiveness and field irregularities whereby the material isuniformly applied to the entire surface area of the field. Moreover, theGNSS-derived positioning and heading information can be compared toactual positioning and heading information derived from other sensors,including gyros, for further calibration.

IV. Multi-Antenna High Dynamic Roll Compensation and Rover L1 RTK

Another alternative aspect GNSS guidance system 602 is shown in FIGS. 11and 12 and provides high dynamic roll compensation, heading andrate-of-turn (ROT) in an RTK system including a GNSS receiver 604including an RF converter 606 connected to a multi-channel trackingdevice 608 and first and second antennas 610, 612, which can be mountedon top of a vehicle 10 in fixed relation defining a tranverse (X axis)fixed baseline 614. The receiver 604 provides a GNSS data output to aguidance processor (CPU) 616, which includes a GUI/display 618, amicroprocessor 620 and media (e.g., for data storage) 622. A steeringvalve block 624 includes autosteer logic 626, hydraulic valves 628 andsteering linkage 630. A wheel sensor 632 is connected to the steeringvalve block 624, which in turn is connected to the guidance processor616 by a suitable CAN bus 634.

GNSS positioning signals are received from a constellation of GNSSsatellites and an RTK base transceiver 636, which includes a receiver638 and a transmitter 640 for transmitting carrier phase signals to arover RTK receiver 642. By using GNSS positioning signals from thesatellites and correctional signals from the RTK base transceiver 636,the guidance system 602 can calculate a relatively accurate positionrelative to the base transceiver 636, which can be located at apredetermined position, such as a benchmark. The guidance system 602described thus far is an RTK system utilizing a dual frequency receiverand is capable of achieving sub-centimeter accuracy using the carrierphase signals.

Roll compensation, heading and rate of turn can all be calculated usingvector-based heading (yaw and roll) information derived from the roverGNSS receiver 604. High-dynamic vehicle roll is a problem with certainapplications, such as agricultural vehicles, which traverse uneventerrain and tend to be relatively tall with antennas mounted threemeters or more above ground level. Antenna arrays can swing significantdistances from side to side with vehicle roll, as indicated by a rollarrow 644. Such deviations can be detrimental to precision farming, andrequire compensation. The fixed-baseline vehicle antennas 610, 612provide the necessary dynamic vector outputs for processing andcompensation by the steering valve block 624. For example, themicroprocessor 620 can be preprogrammed to instantly respond to suchroll errors by providing counteracting output signals via the CAN bus634 to autosteer logic 626, which controls the hydraulic valves 628 ofthe steering valve block 624. A slight delay phase shift can beprogrammed into the microprocessor 620, thus reflecting the inherent lagbetween vehicle roll and the steering system reaction. The delay phaseshift can be adjustable and calibrated for accommodating differentequipment configurations. The GNSS receiver 604 output providesrelatively accurate guidance at slow speeds, through turns and inreverse without relying on sensing vehicle motion via an inertialnavigation system (INS), utilizing gyroscopes and/or accelerometers.Moreover, the guidance system 602 can eliminate the calibrationprocedures normally needed for INS-corrected systems.

The system 602 can likewise provide high dynamic yaw compensation foroscillation about the vertical Z axis using the two-antenna fixedbaseline configuration of the receiver 604. Adding a third antenna wouldenable high dynamic compensation with respect to all three axes XYZe.g., in a six-degrees-of-freedom mode of operation.

Providing multiple antennas 610, 612 on a rover vehicle 10 cansignificantly improve the ability to resolve integer ambiguities byfirst obtaining an attitude solution by solving for the locations of therover antennas 610, 612 with respect each other. Then, using thenon-relative locations and the known relative ambiguities, solving forthe global ambiguities using observations taken at each antenna 610,612. The number of observations is thus significantly increased overconventional RTK. Solving the global ambiguities enables locating therover antennas 610, 612 in a global sense relative to a base station636. Using multiple antennas in this manner enables using L1 singlefrequency receivers, which tend to be less expensive than dual frequency(L1 and L2) receivers, as in conventional RTK systems. An exemplarymethod consists of:

-   -   1. Transmitting code and carrier phase data from a base station        636 to a multiple antenna rover system (e.g., 602).    -   2. At the rover 602 side, determining the relative locations and        the relative ambiguities of the multiple antennas using an        attitude solution taking advantage of known geometry constraints        and/or a common clock. Such a method is disclosed in U.S. Pat.        No. 7,388,539, which is assigned to a common assignee herewith        and is incorporated herein by reference.    -   3. Optionally store off the attitude solution (locations and        ambiguities) for later time-tag matching with the data from the        base station 636. Optionally, also store off the current GNSS        observations (carrier phase) for the same purpose. Although this        step is not necessary, time tag matching of base and rover data        improves results by avoiding extrapolation errors.    -   4. Form single or double difference equations and solve for the        global ambiguities using knowledge of the relative antenna        locations and/or common clocks and/or the relative ambiguities.

Example using a two-antenna rover system (e.g., 602):

-   -   At antenna 1 (e.g., 610) of the rover, we can write the equation        R1=[A]x1−N1,    -   where R1 is a carrier phase observation vector (single or double        difference) at antenna 1, A is a design matrix, X1 is the        location vector of antenna 1 (may include clock if single        differencing is used), and N1 is an ambiguity vector for antenna        1.

Similarly, at antenna 2 (e.g., 612) we can writeR2=[A]x2−N2

-   -   Where R2 is a carrier phase observation vector at antenna 1, A        is a design matrix, X2 is the location vector of antenna 2, and        N2 is an ambiguity vector for antenna 2.    -   Note, that in this example, the design matrix A is taken to be        the same in both antenna equations. But, this is true only if        both antennas see the same satellites. A more general example        would use separate A1 and A2 for the two equations.    -   Solving an attitude solution (for example, see U.S. Pat. No.        7,388,539), we find the relative antenna displacement V, and the        relative ambiguity M where        V=x2−x1        and        M=N2−N1

Thus, combining the above equations, we haveR1=[A]x1−N1R2=[A](x1+V)−(N1+M)

Rearranging givesR1=[A]x1−N1R2[A]V+M=[A]x1−N1

And, combining into a single vector equations givesR=[A]x1−NWhereR=[R1,R2−[A]V+M] ^(T) and N=[N1,N1]^(T)

Where ‘T’ denotes transpose

Referring to the above example, twice as many equations are obtained forthe same number of unknowns (e.g. X1 and N1). Solving for the globalinteger ambiguity N1 is facilitated by the multiple available equations.

Multiple antennas can also be utilized at the base and would provide theadvantage of canceling multipath signals. However, multiple antennas onthe rover are generally preferred because they provide attitude for therover 10, which is generally not of concern for the base 636.

V. Moving Baseline Vehicle/Implement Guidance Systems

Alternative embodiment multiple-antenna GNSS guidance systems are shownin FIGS. 13-18 and utilize a moving baseline between a vehicle-mountedantenna(s) and an implement-mounted antenna. Independent implementsteering can be accomplished with a powered, implement steering systemor hitch, such as those shown in U.S. Pat. No. 6,865,465, No. 7,162,348and No. 7,373,231, which are assigned to a common assignee herewith andare incorporated herein by reference.

FIGS. 13-14 show a GNSS guidance system 726 comprising another modifiedembodiment of the present invention and including a vehicle 10 connectedto an implement 728 by a hitch 730. The hitch 730 permits the implement728 to move through three axes of movement relative to the vehicle 10 asthe system 726 maneuvers and traverses ground with irregularitiescausing the vehicle 10 and the implement 728 to yaw, pitch and rollsomewhat independently of each other. A moving baseline 732 is definedbetween points on each, e.g., between a vehicle antenna 753 and animplement antenna 756. The moving baseline 732 is generally a 3D vectorwith variable length and direction, which can be derived from thedifferences between the vehicle antenna 753 location (X1, Y1, Z1) andthe implement antenna location (X3, Y3, Z3), or other predeterminedpoint locations on the vehicle 10 and the implement 728. The guidancesystem 726 includes a single GNSS receiver 734 (e.g., a single printedcircuit board (PCB) receiver) receiving ranging data streams from theantennas 753, 756, which can include the normal front end RFdownconverter components. Using the geodetic-defined position solutionsfor the antennas 753, 756, the moving baseline 732 is defined and usedby a guidance CPU 736 in real-time for computing guidance solutions,which include steering command outputs to the steering valve block 738.The varying separation of the antennas 753, 756 occurs both at the startof attitude acquisition and during operation.

FIG. 15 shows another alternative aspect vehicle/implement GNSS guidancesystem 740 with first and second vehicle antennas 753, 754, which caninclude front end down converter RF components providing ranging signaloutputs, along with the implement antenna 756, to the single GNSSreceiver 734 as described above. The vehicle antennas 753, 754 define afixed baseline 754 by their respective positions (X1, Y1, Z1), (X2, Y2,Z2), which function to provide vector heading and rate-of-turn (ROT)output information. Such positioning data is input to the guidance CPU736 by measuring yaw and roll attitudes whereby such guidance andperformance information can be determined solely on GNSS-defined rangingdata utilizing the fixed-relationship mounting of the vehicle antennas753, 754 on the vehicle 10. Such information can be processed inconnection with the implement antenna 756 position information in orderto provide more complete GNSS positioning and guidance solutions,including travel paths for the vehicle 10 and the implement 728.

FIG. 16 shows another modified aspect GNSS positioning system 752, whichincludes first and second vehicle antennas 753, 754 at GNSS-definedpositions (X1, Y1, Z1), (X2, Y2, Z2) respectively, which positionsdefine a vehicle fixed baseline 755. The implement 728 includes firstand second implement antennas 756, 757 at GNSS-defined positions (X3,Y3, Z3), (X4, Y4, Z4) respectively, which define an implement fixedbaseline 758 and from which the guidance CPU 736 determines heading andROT for the implement 728 using similar vector techniques to thosedescribed above. A movable baseline 759 can be defined between a vehicleantenna 753 and an implement antenna 756 as shown, or between othercorresponding antenna pairs, or other predetermined locations on thevehicle 10 and the implement 728. The system 752 utilizes a single GNSSreceiver 734 receiving input ranging information from the four antennas753, 754, 756, 757 and providing a single output stream to the guidanceCPU 736. It will be appreciated that various other antenna/receivercombinations can be utilized. For example, a third vehicle and/orimplement antenna can be provided for 3-axis attitude computation. INScomponents, such as gyroscopes and/or accelerometers, can also beutilized for additional guidance correction, although the systemsdescribed above can provide highly accurate guidance without such INScomponents, which have certain disadvantages.

FIG. 17 shows the 2+1 antenna system 740 operating in a guidance modewhereby a predetermined number of positions 790 at predeterminedintervals are retained by the guidance CPU 736, thereby defining amulti-position “breadcrumb” tail 792 defining the most recent guidepathsegment traversed by the vehicle 10 based on the locations of thevehicle antenna(s) 753 (754). Although the 2+1 antenna guidance system740 is used as an example, the 1+1 antenna guidance system 726 and the2+2 guidance system 752 can also be used in this mode and function in asimilar manner, with more or less ranging signal sources. The guidanceCPU 736 utilizes the retained tail “breadcrumb” positions 790 inconjunction with the GNSS-derived antenna locations for computing acrosstrack error representing implement 728 deviation from a desiredguidepath 794, and the necessary steering signals for correcting thevehicle 10 course to maintain the implement 728 on track. Still further,in a multi-position tail 792 operating mode the high dynamic rollcompensation function described above can be utilized to compensate forvehicle and/or implement roll using the fixed baseline(s) 746, 755, 758for further guidance solution accuracy based solely on GNSS ranginginformation.

With the systems 726, 740 and 752, a single receiver can be used forachieving carrier phase relative accuracy, even without differentialcorrection. A single clock associated with the receiver facilitatesambiguity resolution, as compared to dual receiver and dual clocksystems. Direct connections among the components further enhanceaccuracy and facilitate high dynamic roll corrections, as describedabove. Continuous base and rover ranging data are available forpositioning and control. With the 2+1 and the 2+2 configurations, thefixed baseline(s) provide heading and ROT guidance for the vehicleand/or the implement. Steering control for the vehicle is derived fromcrosstrack error computations utilizing the multiposition tail 792.

FIG. 18 is a schematic block diagram showing the components of the GNSSguidance systems 726, 740 and 752. The vehicle 10 components include aGNSS receiver 734 including a first vehicle antenna 753, an optionalsecond vehicle antenna 754, an RF down converter 764, a tracking device766 and an optional rover RTK receiver 768. A guidance processor CPU 736includes a GUI display 772, a microprocessor 774 and a media storagedevice 776. Vehicle steering 778 is connected to the guidance processorCPU 736 and receives steering commands therefrom. GNSS-derived data istransferred from the GNSS receiver 734 to the guidance processor CPU736. The implement 728 mounts an implement positioning system 780including a first implement antenna 756 and an optional second implementantenna 757, which are connected to the vehicle GNSS receiver 734 andprovide GNSS data thereto. An implement steering subsystem 784 receivessteering commands from the guidance processor CPU 736 via a CAN bus 786.The implement 728 is mechanically connected to the vehicle 10 by a hitch788, which can be power-driven for active implement positioning inresponse to implement steering commands, or a conventional mechanicallinkage. The hitch 788 can be provided with sensors for determiningrelative attitudes and orientations between the vehicle 10 and theimplement 728.

VI. Multi-Vehicle GNSS Tracking Method

FIG. 19 shows a multi-vehicle GNSS tracking system 802 adapted fortracking primary and secondary rover vehicles 804, 806, which cancomprise, for example, a combine and an offloading truck. Otherexemplary multi-vehicle combinations include crop picking and harvestingequipment, snowplows, aircraft engaged in mid-air refueling, etc. Datatransfer among the vehicles 804, 806 and a base transceiver 808 can beaccomplished with short-range radio links, such as Bluetooth and Wi-Fiwireless technologies. For example, the base transceiver 808 cantransmit corrections to the rovers 804, 806 at predetermined intervalsof one second (i.e., 1 Hz).

Between the base transmissions the primary rover 804 can transmit itsidentifying information (ID) and GNSS-derived position and timinginformation to the secondary rover 806. The secondary rover 806 thusreceives both differential corrections and the primary rover data overthe same radio link, or through an additional radio link. Such data cancomprise a multi-position tail 810 as described above and against whichthe secondary rover 806 can guide. For example, the secondary rover 806can directly follow the primary rover 804 at a predetermined distance byaligning its travel path with the multi-position tail 810 at apredetermined following distance, or it can offset its own paralleltravel path a predetermined offset distance, as shown in FIG. 19. Thesecondary rover 806 can position itself relative to the primary rover804 based on either a predetermined time interval or a predeterminedseparation distance. As discussed above, the multi-position tail 810 canautomatically update whereby only a predetermined number of detectedpositions are stored, which can correspond to a predetermined timeduration or distance behind the primary rover 804 c.

FIG. 20 shows a schematic block diagram of components comprising themulti-vehicle tracking system 802. The onboard systems for the primaryrover 804 and the secondary rover 806 can be similar to thevehicle-based GNSS guidance systems described above, with the additionof an inter-rover radio link 812.

VII. Alternative Embodiment Multi-Antenna System 902

FIG. 21 shows a multi-antenna, GNSS-based guidance system 902 installedon a motive component 904, herein exemplified by a tractor, towing aworking component 906, herein exemplified by a towed implement, andcollectively comprising a vehicle 907. Without limitation, the vehicle907 is configured for agricultural operations. However, the system 902could also be used for guiding and controlling a wide range of vehicles,equipment and machines. For example, the system 902 could be applied toearth-moving equipment, examples of which are shown in U.S. patentapplication Ser. No. 12/857, 298, which is assigned to a common assigneehere with and is incorporated herein by reference. The motive andworking components can be interconnected, articulated components of apiece of equipment, such as the base vehicle and boom assemblycomponents of an excavator. Also shown are the three axes X, Y, and Z,and the positive directions of rotation about those axes, i.e., roll,pitch, and yaw respectively. Using three antennas 952, 954, 956, theGNSS guidance system 902 can track the motive component 904 and workingcomponent 906 in all six degrees of freedom and in relation to eachother. The motive component 904 includes a motive component antenna 952,and the working component 906 includes first and second workingcomponent antennae 954, 956, i.e. a “1+2” configuration. Othertractor/implement antenna combinations could also be used, such as 2+2.This transfers not only positional information to a GNSS guidancecomputer 910, but also data on the slope of the earth below the vehicle907 and whether the working component 906 is traveling laterally(“offset”) compared with the motive component 904, indicating a slidingmotion and crosstrack displacement. In FIGS. 21 and 22 the antennas 952,954, 956 are shown in “normal” positions with the working component 906aligned with and positioned directly behind the motive component 904.The distances between the working component antennas and the motivecomponent antenna can vary depending on the relative orientations ofeither the motive component 904 or the working component 906, or both.

FIG. 22 shows the motive component 904 towing the working component 906with an articulated hitch 914 and a tongue 915, and the various attachedsensors and systems which create an embodiment of the guidance pathmemory system 902. The GNSS system includes the antennas 952, 954, 956,a GNSS receiver 908, a guidance computer 910 including amicroprocessor/CPU 909, a working component computer 913 including amicroprocessor/CPU 923 and a graphical user interface (GUI) 911. Thisembodiment of the present invention uses differential GNSS (DGNSS) byusing a base station 922 located generally in the vicinity of the workto be performed (FIG. 24). The base station 922 includes an antenna 924,a base receiver 926 and a base transmitter 927. The base and roverconfiguration is similar to other differential (DGNSS) guidance systems,such as the Outback S Series produced by Hemisphere GPS LLC of Calgary,Canada. The GNSS components are preferably configured to use carrierphase GNSS signals with a base-and-rover receiver combination, which isgenerally referred to as real-time kinematic (RTK). See U.S. Pat. No.6,469,663, which is incorporated herein by reference. The guidancesystem 902 will track the three-dimensional position of the motivecomponent 904 and the working component 906, along with the roll, pitch,and yaw (collectively attitude) of the motive component 904 and theworking component 906, both independently and relative to each other.Additionally, the GNSS system 902 will determine the heading of themotive component 904, and will detect when the working component 906 isfacing a different heading from the motive component 904 or if theworking component 906 is moving laterally compared with the motivecomponent 904, inferring that the working component 906 may have becomemisaligned due to a bump in the path or because the path is along aslope.

Also shown in FIGS. 22, 24 and 25 are several sensor devices fordetecting other vehicle parameter values. These sensors include variousvehicle sensors 912, a wheel compaction PSI sensor 916, a hitch feedbacksensor 920, and various working component sensors 918. The variousvehicle sensors 912 include a motive component wheel angle sensor 935,ground speed sensor 936, fuel sensor 937, RPM sensor 938, and variousother optional sensors that detect variables of vehicle performance andmay enhance the information received about the terrain being drivenover. The various working component sensors 918 include a ground speedsensor 988, a working component wheel angle sensor 989, and compressionsensors 990 for determining the amount of soil being compressed similarto the wheel compaction PSI sensor 916. The information harvested fromthese various sensors is taken and combined with the positional datareceived by the GNSS system 902, and finally computed by the guidancecomputer 910. The information is output to an external computer 934, asshown in FIG. 25, where it can be analyzed and future pre-planned pathscan be designed based on the data gathered during the field pass.

Alternatively, the guidance computer 910 could calculate and modify itsown stored, pre-planned path based on the gathered data and programmedfunctions for dealing with different field conditions. The guidancecomputer 910 can be pre-programmed to adapt to field conditions indifferent ways depending on the circumstances. For example, themicroprocessor 909 can be programmed to instruct an articulated hitch914 that is included with an optional motorized component, such as thedevice covered by previously mentioned and incorporated U.S. Pat. No.7,162,348, to adjust the position of the working component 906 relativeto the motive component 904 depending on the severity of the slope asthe vehicle 907 is traversing that slope. The computer 910 will updatecommands to the hitch 914 as data is reported by working component andmotive component gyro sensors 921, 919 and other relevant sensors fordetecting a change in pitch or roll. All of this can be performed inreal time as data is reported to the guidance computer 910. The conceptof real-time, pre-planned path modification for the present inventionfollows similar techniques as described in U.S. Patent Publication No.2007/0021913, which is assigned to a common assignee herewith andincorporated herein by reference.

Also located on the motive component 904 is a steering controller 917receiving steering commands from the guidance computer 910 and applyingthem to the motive component 904, steering it around the field. Theguidance computer 910 also controls the power settings of the motivecomponent 904, reducing or increasing speed, and optionally controlsother vehicle 907 operations, e.g., adjusting the stiffness of shockabsorbing components via adjustable hydraulic shock absorbers 958. Acontroller for controlling the amount of shock absorbed by the hydraulicshock absorbers 958 can be connected directly to and controlled by theguidance computer 910. This will allow the vehicle to increase theresistance of the shock absorbers 958 prior to the vehicle traversing aparticularly rough terrain, or decrease their resistance for softerterrain, depending on performance desired from the vehicle 907.Similarly, other elements of the vehicle can be controlled in this way,which will lead to increased vehicle performance and control.

The use of a moving baseline 998 between at least three antennas 952,954, 956, with two antennas located on the working component 906 and atleast one on the motive component 904, allows the guidance system 902 totrack the position of the working component relative to the motivecomponent. The working component 906 may actually roll in one directionwhile the motive component 904 rolls in the opposite direction.Including additional data provided by a motive component inertialmeasurement unit (IMU) 919 and a working component IMU 921 allows theguidance computer 910 to distinguish yaw, pitch, and roll movement ofthe working component 906 relative to yaw, pitch, and roll movement ofthe motive component 904. Because the working component 906 is doing theactual work in a field, it is important to ensure that the workingcomponent 904 is being properly guided and aligned relative to themotive component 906. The use of an optional motorized hitch 914, asmentioned above, allows the guidance computer 910 to readjust andrealign the working component 906 if the guidance system detects that itis no longer properly aligned. This optional aspect is further discussedin the previously mentioned and referenced U.S. Patent Publication No.2009/0164067.

FIG. 23A demonstrates the relationship among the three antennas' 952,954, 956 positions. Using basic trigonometric equations, unknowndistances between antenna pairs can be solved and used by the guidancecomputer 910 to recalculate driving directions. The motive componentantenna 952 location is denoted by A. The working component antennas B(954) and C (956) are located a fixed distance BC away from each other.The point where the hitch 914 pivots, allowing the working component 906to rotate independent from the motive component 904, is at point F. Thepivot arm is alternatively labeled the tongue 915. A point-of-interest(POI) directly below the motive component-mounted antenna. Point E is apoint directly between the two working component-mounted antennas 954,956.

The known distances include the distance between the workingcomponent-mounted antennas (BC) and the height (H) of the motivecomponent-mounted antenna 952 above the working component-mountedantennas 954, 956. When the working component is directly behind themotive component, as depicted in FIG. 23A, and points B and C are atapproximately the elevation of the point of interest (POI), severalright-isosceles triangles are formed and the distances among theantennas can be computed.

FIGS. 23B and 23C show the trigonometric relationship changes when theworking component 906 rotates about point F (hitch 914) via the tongue915. The working component will shift in a direction along the X-Yplane, changing the moving baseline relationship AB and AC.

FIG. 23C demonstrates the positional relationship between the motivecomponent-mounted antenna 952 at A and the working component-mountedantenna 956 at C as it moves from the starting position shown in FIG.23A and moves to the ending position shown in FIG. 23B. The height ‘h’is known, and the X, Y, and Z coordinates of both point A and point Care known. The coordinates of the Point of Interest (POI) are:(X ₁ ,Y ₁ ,Z _(1.1))=(X ₁ ,Y ₁ ,Z ₁ −h)

Because point C and POI are at the same elevation, Z_(1.1)=Z₃. Thus, thedistances d and d.1 can be calculated:d=√[(X ₃ −X ₁)²+(Y ₃ −Y ₁)²]d.1=√[(X _(3.1) −X ₁)²+(Y _(3.1) Y ₁)²]And therefore:Tan θ=h/dTan θ.1=h/d.1AC=h/Sin θAC.1=h/Sin θ.1Alternatively:AC=√[(X ₃ −X ₁)²+(Y ₃ −Y ₁)²+(Z ₃ −Z ₁)²]AC.1=√[(X _(3.1) −X ₁)²+(Y _(3.1) −Y ₁)²+(Z ₃ −Z ₁)²]Sin θ=h/ACSin θ.1=h/AC.1This alternative formula can be used because the three-dimensionalpoints A and C can be determined by their actual GNSS positions asdetermined by GNSS satellite signals received by the various antennas952, 954, 956.

This same method can be used as long as points B, C, and POI are at thesame elevation; e.g. Z_(B)=Z_(C)=Z_(POI), leaving Φ to equal 90°. Thedistances AB and AC will vary as the working component 906 is rotatedabout point F as shown in FIG. 22C. Using the formulas above, thedistances AB and AC can always be determined as long asZ_(B)=Z_(C)=Z_(POI).

The working component 906 and the motive component 904 can independentlyroll (X-axis), pitch (Y-axis) and yaw (Z-axis) relative to each other.For example, rolling and pitching will alter the elevation of points B,C, and POI relative to each other because the motive component 904 andthe working component 906 will not be coplanar. The above-mentionedequations will not be able to solve the distances AB and AC. Also, theangle Φ has changed to Φ′, which is no longer a right angle. In such aninstance, the height h will not change, however, and the distancesbetween points can still be calculated usingAB=√[(X_(B)−X_(A))²+(Y_(B)−Y_(A))²+(Z_(B)−Z_(A))²] orAC=√[(X_(C)−Y_(A))²+(Z_(C)−Z_(A))²+(Z_(C)−Z_(A))²]. The various anglescan then be calculated using the law of cosines:

$\frac{{{Cos}\;\Phi^{\prime}} = {h^{2} - {A\; C^{2}} - d^{2}}}{{- 2}\left( {A\; C*d} \right)}$

Knowing the lengths of at least two sides and a known angle Φ allowscalculation of the other side and angles. This will allow the guidancecomputer 910 to calculate the distance between the antennas 952, 954,956 no matter what the three-dimensional orientation of the workingcomponent is with respect to the motive component. The roll, pitch, oryaw difference between the motive component 904 and the workingcomponent 906 can be determined by including IMUs 919, 921 and measuringthe differences recorded by those IMUs. The IMU measurements willprovide additional values for unknown distances necessary to solve therelative position of the working component 906 in relation to the motivecomponent 904.

FIG. 25 is a block diagram showing the relationship between the varioussensors and the GNSS guidance system. The working component 906 containsits own CPU 913, which collects data from both the working componentsensors 918 and the hitch feedback sensor 920. These elements areseparate to allow the working component 906 to move itself relative tothe vehicle 4 by maneuvering the mechanical hitch 914, which willrealign the working component being towed by the vehicle, as explainedin further detail in U.S. Pat. No. 7,292,186, which is incorporatedherein by reference. The guidance computer 910, on the other hand, isdirectly connected to the GNSS receiver 8, the vehicle sensors 912, andthe wheel compaction sensor 916. A controller area network (CAN) cable932 connects the working computer 913 with the guidance computer 910located in the vehicle 904. Alternatively, the two computers maycommunicate over a local wireless network. The wireless network may belocated somewhere on the vehicle 907 or may be located elsewhere in thevicinity. Such a network typically requires a wireless router and awireless communication device connected to each computer.

Communication between the two computers 910, 913 compares data receivedfrom the various sensors and the GNSS guidance system and results inproblem solving for future pre-planned paths. Problem solving can eitherbe done in real-time, as mentioned above, or used in generating future,pre-planned paths off-site. This may be performed by uploading gathereddata onto an external PC 934 or using the guidance computer 910 directlyto calculate a new path. Field data that has been gathered by thevarious sensors can include, without limitation: the slope of the fieldat various point locations; the speed at which the vehicle previouslynavigated the field; and the GNSS positional data recorded as thevehicle traversed the field, including locations where the workingcomponent 906 and/or the motive component 904 were no longer in linewith the previous pre-planned path. The user may interpret the data andcreate a new pre-planned program based on it, or an optional computerprogram can take the data and generate a pre-planned path based onprogrammed configurations for dealing with different field conditions.

It should be noted that the components of the system 902 can be combinedin various ways and will function in a similar manner. For example, acommonly used component is a combination receiver and antenna unit,sometimes referred to as a “smart antenna.” Other components may alsooptionally be combined, such as the various base station components. Acommon example of such a combination antenna is the A-220 “SmartAntenna” manufactured by Hemisphere GPS LLC of Calgary, Canada, whichare typically combined with Hemisphere GPS receivers and othercomponents, as described in U.S. Patent Application Ser. No. 61/377,355,which is assigned to a common assignee herewith and incorporated hereinby reference.

As mentioned above, a motorized hitch 914 connects the working component6 to the motive component 904. This motorized hitch contains a feedbacksensor 920 which communicates with the working component computer 913,which in turn communicates with the guidance computer 910. This allowscommands to be sent to the motorized hitch 914 from the guidancecomputer 910 regarding positioning of the working component 906, andfeedback data to then be reported to the guidance computer 910 forrecording and additional guidance commands. Stresses on the hitch 914from holding the working component 906 along a slope and relativeposition to the motive component 904 are among the variables reported tothe guidance computer 910 by the hitch feedback sensor 920.

FIG. 25 is a block diagram dividing the separate sub-systems of thesystem 902. FIG. 25 shows the flow of information from the sensors andGNSS positional system to a finished form of field output data 928 as itis gathered by the various sensors located on the motive component 904and the working component 906 and communicated between the workingcomponent computer 913 and the guidance computer 910. The varioussensors including the vehicle sensors 912, wheel compaction psi sensor916, working component sensors 918, and hitch feedback sensor 920 feedinto the guidance computer 910. Additionally, the antennas 952, 954, 956receive satellite positional information and transmit that informationto the GNSS receiver 908 which is directly connected to the guidancecomputer 910. The guidance computer 910 is connected to the GUI 911which both displays information to the user and allows for user inputvia an interface device, such as a touchscreen display or otherinterface device. Finally, the field output data 928 is created bycombining the entirety of the recorded data and relating it to thelayout of the field or piece of land that has been worked. This willallow for a more efficient and accurate pre-planned path the next time avehicle 904 is to work the field in question by combining the data andconfiguring an automatic steering program focused on guiding the vehiclewhile addressing the landscape concerns. Knowing where fieldirregularities are located is the easiest way to ensure the vehicle 907correctly navigates these irregularities.

The guidance computer 910 can interface with an external computer (e.g.,PC) 934 which can receive recorded field data, edit that data, and turnthat data into a pre-planned guidance path. Input field data 930 is dataincludes pre-planned path and controller data. This data is installed inthe guidance computer 910 and actively and automatically guides andcontrols the vehicle through interaction with the steering controller917. The steering controller 917 will take guidance commands, steeringcommands, and other commands to control various vehicle functions andwill physically perform those functions. Thus a preplanned path based onearlier field data will know to slow down when the motive component isapproaching a particularly sharp curve or may instruct the motorizedhitch 914 to adjust the position of the working component 906 prior toentering a sloped area.

Output to an external computer 934, such as a personal computer (PC),can be performed in a number of ways. Field data output 928 can bedelivered over a direct connection established between the onboardcomputer 910 and the external computer 934, or field data output 928 canbe offloaded onto a portable storage device and then connected to theexternal computer 934. Similarly, input data 930 can be generated by anexternal (e.g., offsite) computer 934 and stored onto a portable storagedevice, and later uploaded to the CPU 910. Such input data 930 mayinclude a pre-planned driving path for an initial field test, or anupdated planned path based on previous data collection.

The vehicle sensor suite 912 can also include a camera 939, or othersuitable optical device. For example, U.S. Patent Publication No.2009/0204281, which is assigned to a common assignee herewith, shows avideo input system for autosteering control of an agricultural vehicleand other machines. U.S. patent application Ser. No. 12/504, 779, whichis also assigned to a common assignee herewith, shows an opticaltracking vehicle control system and method. Both of these applicationsare incorporated herein by reference. The camera 939 can be directed atthe projected guide path of the tractor 904, towards crop rows on eitherside, along vehicle tracks or towards any area of interest relative tothe tractor 904 or the implement 906. Optical input from the camera 939can be used by the guidance computer 910 for guiding the vehicle 907using video input. Alternatively, the camera 939 can be used forrecording, observing and archiving the path of the vehicle 907 forpurposes of record-keeping or future guidance. For example, in a “matchtracks” mode, it may be desirable for the vehicle 907 to accuratelyretrace previous guide paths, which may be optically observable. Stillfurther, such optical data can be useful for observing the crop plants(typically in rows) whereby the operator and/or the guidance computer910 can avoid driving over crops and can monitor and record theirgrowth. Still further, the camera 939 can be user-controlled andadjustable for visually observing the vehicle 907 guide path or thecrops close-up, for example, on the GUI 911 in the cab.

FIG. 26 shows a plan view of a field with a border 940 and a vehicle 907traversing a pre-planned path 942. The field contains severalirregularities, including a severely sloped section 944, a section ofsoft earth 946 where water or soil type will cause the vehicle andworking component wheels to slightly sink into the ground, an unevenarea 948 which may be rocky or otherwise uneven. The various sensorsattached to the motive component and working component will record dataas the vehicle 907 traverses the areas of irregularity. For instance; asthe motive component approaches the uneven area 948, the wheel sensors916 may detect compression psi differences if the ground contains rocks.Likewise, there may be a sensor attached to the shock absorbers of themotive component to determine the stress levels on said shocks whentraversing such an uneven area. The GNSS guidance system 902 will detectwhether the vehicle 904 or working component 906 rolls or pitches to aside, or if the heading is altered due to a bump. If the effects of theuneven ground result in the vehicle 907 being deflected off course, theguidance CPU can record this information and instruct the vehicle toslow down in that location at a future date.

The measurement of the varying distance of the three GNSS antennas 952,954, 956 from one another, a plurality of satellites, and the basestation 922 along with heading, attitude, motive component speed, motivecomponent gearing, power, fuel consumption, working component load,stress loads, and other factors which may affect vehicle progressionthrough a field will result in providing knowledge to an extreme detailof the field or piece of land being driven. Once all measurements aretaken, the end-user will be able zoom in on any particular spot in afield map and view near topographic details of any location. Knowingwhere rocks, slopes, and obstacles are and controlling the vehicleaccording to this knowledge will result in greater efficiency, less wearon the vehicle and working component, and lower costs on vehicle fuel aswell as seeds, chemicals, and other products being distributed.

Recording field conditions in a variety of weather types and a varietyof soil types can also increase efficiency and safety. For instance; ifthe field needs to be worked while it is raining, preplanned path datacan be fed to the guidance computer 910 from a previous field pass fromwhen it was raining. This will present a completely customizable methodof vehicle guidance and control which can be optimized depending onweather type, vehicle type, soil condition, and other factors.

A preferred embodiment of the present invention will result in betterpositioning of the motive component 904 for improved working component906 position, attitude, and track. The hitch feedback sensor 920 willprovide feedback regarding working component attitude and will aid inadjusting a skewed heading. Real time and post analysis of motivecomponent and working component stress areas in the field will result inresolving those areas with additional field preparation or alternationsto the motive component's tires, speed, or power. Generation of databased off of stressed field conditions will allow future passes tosupply guidance changes to preempt working component track distortionsin difficult field conditions. Applying the preferred embodiment to asystem using adjustable variable rate controllers for applying chemical,seed, or other material to a field will result in a guidance system withunparalleled accuracy.

FIG. 27 is a flowchart demonstrating an embodiment of a method ofpracticing the present invention. This embodiment does not contain allpossible sensor data, but instead represents an example of an embodimentof the present invention. The method of practicing the memory system 902starts at 960. The guidance computer 910 is loaded with a pre-plannedvehicle guidance path at 962. All vehicle sensors are initiated andrecord mode begins at 964. From there, the vehicle is automaticallyguided around the selected field at 966. This is either done usingautomatic steering or by directing a driver using a light track bar orother typical guidance method. Alternatively, the vehicle 907 may bedriven manually around the field with the sensors recording data,without the need of a preplanned path or vehicle guidance process.

The various vehicle and working component sensors are constantlychecking the various systems of the vehicle 907. Simultaneously, theGNSS guidance subsystem is recording position and orientation data ofthe vehicle as it travels upon the pre-planned path. When one of thevarious sensors detects a change in the field at 968, the system 902stores data to a storage device such as a hard drive connected to theguidance CPU 910 in the form of a reference point at 970. This referencepoint data includes vehicle speed, vehicle position, vehicleorientation, power output, and any other base system sensor desired tobe recorded by the end user. This reference data is important forcalculating what has occurred at the particular point in the field wherea sensor has picked up a change in the field layout according to thepre-planned path.

At 972 is a check to determine whether the sensors have determined ifthe working component has moved off of the guide-line 942 by an amountpre-set by the user. If the response to this check is “yes,” the system902 records the distance the working component has moved off of theguide-line at 974. From there, the system 902 can optionally re-alignthe working component via the connected motorized hitch 914 at 976. Theuser may wish not to re-align and determine the full effect of the fieldirregularity on the pre-planned guidance path, in which case theoptional step at 976 can be ignored. The method will then loop back tothe guidance step at 966, where sensor checks will continue.

If, at 972, the sensors do not determine the working component hasdrifted off of the guide-line 942, then the method proceeds to the nextcheck-step. This step involves the wheel PSI compaction sensor at 978,wherein the wheel compaction sensors of the working component, themotive component, or both determine that the soil beneath the tire haschanged in some fundamental way. If the answer to this check is a “yes,”then the compaction data is recorded at 980 in reference to positionaldata and orientation data. From there, the system 902 can optionallyslow the vehicle at 982 in order to compensate for the irregular soiltype and ensure a smoother and more accurate ride by the vehicle 907.From here, the method loops back to the guidance step at 966, wheresensor checks will continue.

A constant “vehicle shutoff” check is present in the loop at 984. If thevehicle or system is ever shutoff, it will result in the system endingat 986.

The guidance computer 910 of the present invention can use guidancealgorithms in common with U.S. Patent Publication No. 2009/0164067(incorporated herein by reference) for position determination in amultiple antenna moving-baseline guidance system. Position and guidancealgorithms used by the processors of the present invention are wellknown and documented in the prior art.

VIII. Alternative Embodiment Multi-Antenna System 1002

A guidance system 1002 comprising an alternative embodiment of thepresent invention is shown in FIG. 28 and includes a motive component(e.g., tractor) 904 substantially as described above. Without limitationon the generality of articulated working components adapted for use withthe present invention, an articulated implement 1006 is shown with firstand second implement sections 1006A and 1006B, which are adapted forrotating relative to each other around a hinge line 1009 extendinggenerally parallel to the X axis. Alternatively, various other workingcomponents, such as machines, earthworking equipment, articulatedexcavator booms, motor graders and agricultural implements can beutilized with the system 1002. For example, a wide range of tillage,cultivating, harvesting, seeding and spraying implements can becontrolled with the system 1002. Such implements include side-by-sideand front-and-back components, which can be pivotably connected byhinges and other articulated connections, such as hitches.

As shown in FIG. 28, the implement sections 1006A, 1006B can accommodatefield conditions requiring independent rotation. For example, implementsection 1006A can be positioned on a sloping ground surface, such as aterrace, while the other implement section 1006B can be relatively flat.

The guidance system 1002 can utilize multiple antennas for independentlymonitoring positional and attitude (orientation) data from the tractor904 and the implement sections 1006A, 1006B. For example: the tractor904 can be provided with an antenna 952; the first implement section1006A can be provided with antennas 1054, 1055; and the second implementsection 1006B can be provided with antennas 1056, 1057. Respective XYZGNSS-based coordinates can be read from each antenna for computing theirrespective positions, either on an absolute or relative basis. The firstimplement section antennas 1054, 1055 define a first fixed baseline1096A and the second implement section antennas 1056, 1057 define asecond fixed baseline 1096B. Variable baselines 1098 are defined betweenthe tractor antenna 952 and the implement antennas 1054-57. Althoughspecific antenna configurations are shown, they are not limiting and thepresent invention generally contemplates the use of multiple antennas invarious suitable multiples, distributions and configurations.

The position/attitude determining algorithms used by the guidancecomputer 910 can be programmed for the baseline constant and variablefactors for use in computing position/attitude solutions. For example,the guidance computer 910 can include a switching function for switchingamong the antennas in order to optimize the available GNSS ranginginformation. See, U.S. Patent Publication No. 2004/0212533, which isincorporated herein by reference. The availability of ranginginformation from multiple antennas can be important in compensating forGNSS signal blockage, for example, when equipment or environmentobstructions prevent individual antennas from “seeing” enoughsatellites. Interference, multipath and other error sources can lead toposition dilution of precision (“PDOP”). These conditions can becompensated for by the multi-antenna configuration shown in FIG. 28. Ofcourse, the tractor 904 can also be equipped with multiple antennasdefining additional fixed and variable baselines. Multiple antennas arealso useful for computing “Vector” guidance solutions comprising objectattitude or orientation, direction of travel (heading) and velocity.

While the description has been made with reference to exemplaryembodiments, it will be understood by those of ordinary skill in thepertinent art that various changes may be made and equivalents may besubstituted for the elements thereof without departing from the scope ofthe disclosure. In addition, numerous modifications may be made to adaptthe teachings of the disclosure to a particular object or situationwithout departing from the essential scope thereof. Therefore, it isintended that the claims not be limited to the particular embodimentsdisclosed as the currently preferred best modes contemplated forcarrying out the teachings herein, but that the claims shall cover allembodiments falling within the true scope and spirit of the disclosure.

Having thus described the invention, What is claimed as new and desiredto be secured by Letters Patent is:
 1. A GNSS-based method ofcontrolling a machine comprising a prime component and an auxiliarycomponent interconnected by an articulated connection, which methodcomprises the steps of: equipping said machine with a GNSS systemincluding a GNSS receiver receiving GNSS ranging signals; providing saidGNSS system with multiple antennas connected to said receiver; mountingat least one of said antennas on said prime component; mounting multiplesaid antennas on said auxiliary component; forming a fixed baseline onsaid auxiliary component between said auxiliary component antennas;forming variable baselines between said prime and auxiliary componentantennas; equipping said machine with a guidance computer; connectingsaid guidance computer to said GNSS receiver; inputting to said guidancecomputer information corresponding to said fixed and variable baselines;and pre-programming said guidance computer to position at least one saidcomponents using said fixed and variable baseline information.
 2. Themethod of claim 1, which includes the additional step of: moving saidauxiliary component relative to said prime component through 3 axes ofmovement corresponding to roll (X), pitch (Y) and yaw (Z) through saidarticulated connection.
 3. The method of claim 2, which includes theadditional step of: adjusting said component relative positions in realtime and in response to said baseline information.
 4. The method ofclaim 3, which includes the additional steps of: preprogramming saidcomputer with a guide path of movement for said auxiliary component; andguiding said auxiliary component along said preprogrammed path ofmovement.
 5. The method of claim 4, which includes additional steps of:providing a vehicle operating parameter sensor on said vehicle andconnected to said guidance computer; and correcting said guide pathusing said GNSS-defined positions and said vehicle operating parameters.6. The method of claim 5, which includes the additional steps of:providing a prime inertial measuring unit (IMU) on said prime component;providing an auxiliary IMU on said auxiliary component; outputting fromsaid IMUs signals corresponding to roll (X), pitch (Y) and yaw (Z)movements of said prime and auxiliary components; inputting said IMUsignals to said computer; and computing guide path corrections for saidprime and auxiliary components using said IMU signal inputs.
 7. Themethod of claim 5 wherein said operating parameter sensor comprises acamera mounted on said prime component and direct towards said guidepath.
 8. The method of claim 1, which includes additional steps of:providing a switching circuit connected to said antennas and to saidreceiver; switching among said antennas with said switching circuitwhereby respective antennas are selectively connected to said receiver;providing GNSS-based ranging signal inputs to said computer based onrelative positions of said antennas selected by said switching circuit;and selecting said antennas with said computer based on GNSS-basedsignal quality characteristics.
 9. The method of claim 1, which includesthe additional steps of: providing said auxiliary component with firstand second sections; hingedly connecting said first and second auxiliarycomponent sections for movement relative to each other; mountingmultiple said auxiliary component antennas on each said auxiliarycomponent section; forming a variable baseline between each saidauxiliary component antenna and said prime component antenna; andguiding said auxiliary component based on the relative positions of saidauxiliary component sections with respect to each other, said primecomponent and the guide path.
 10. The method of claim 1, which includesthe additional steps of: providing an external computer; connecting saidguidance computer to said external computer; transferring field datainput from said external computer to said guidance computer; andtransferring field data output from said guidance computer to saidexternal computer.
 11. A GNSS-based method of guiding a vehiclecomprising a motive component and a working component interconnected byan articulated hitch, said working component comprising multiplehingedly interconnected sections, which method comprises the steps of:equipping said vehicle with a GNSS guidance system including a receiver,a guidance computer on the motive component and connected to thereceiver, and a working component computer on the working component andconnected to the guidance computer; mounting a motive component antennaon the motive component and connected to the receiver; mounting firstand second working component antennas in spaced relation on each saidworking component section and connected to the receiver; defining afixed-distance, static baseline between the working component antennas;defining first and second variable-distance, moving baselines betweenthe motive component antenna and the first and second working componentantennas respectively; providing a prime inertial measuring unit (IMU)on said motive component; providing an auxiliary IMU on said workingcomponent; outputting from said IMUs signals corresponding to roll (X),pitch (Y) and yaw (Z) movements of said motive and working components;inputting said IMU signals to said guidance computer; computing guidepath corrections for said motive and working components using said IMUsignal inputs; defining a guide path with GNSS-based positions; storingsaid guide path in said guidance computer; navigating a field with saidvehicle; receiving GNSS signals with said working component antennas;computing GNSS-defined positions of said working component antennas withsaid guidance computer; guiding said vehicle along said guide path usingsaid GNSS-defined positions; guiding said working component based on therelative positions of said working component sections with respect toeach other, said prime component and the guide path; providing a vehicleoperating parameter sensor on said vehicle and connected to saidguidance computer; computing guide path corrections for said motive andworking components using said IMU signal inputs; and correcting saidguide path using said GNSS-defined positions and said vehicle operatingparameters.
 12. A GNSS-based system for controlling a machine comprisinga prime component and an auxiliary component interconnected by anarticulated connection, which system includes: a GNSS receiver mountedon the machine and receiving GNSS ranging signals; a prime componentGNSS antenna mounted on the prime component and connected to thereceiver; a pair of auxiliary component GNSS antennas mounted on theauxiliary component and connected to the receiver; multiple variablebaselines each extending between said prime component antenna and arespective auxiliary component antenna and having variable lengthscorresponding to relative orientations of said prime and auxiliarycomponents; a fixed baseline extending between said auxiliary componentantennas; and a computer mounted on said machine and connected to saidreceiver, said computer computing position solutions for said prime andauxiliary components.
 13. The system according to claim 12, whichincludes: said auxiliary component having first and second auxiliarycomponent sections connected by a hinge; and each said auxiliarycomponent section having a pair of GNSS antennas mounted thereon anddefining a fixed auxiliary component antenna baseline extending betweensaid auxiliary component antennas.
 14. The system according to claim 13,which includes: each said auxiliary component section being movablerelative to said prime component through 3 axes of movementcorresponding to roll (X), pitch (Y) and yaw (Z) through saidarticulated connection; one of said variable baselines having variablelengths and orientations corresponding to relative movement of saidcomponents; and said computer being programmed for computing relativepositions and orientations of said prime and auxiliary components inreal time in response to said varying baseline information.
 15. Thesystem according to claim 14, which includes: a prime inertial measuringunit (IMU) on said prime component; an auxiliary IMU on said auxiliarycomponent; output from said IMUs corresponding to roll (X), pitch (Y)and yaw (Z) movements of said prime and auxiliary components; said IMUsignals being input to said computer; and said computer being programmedfor computing guide path corrections for said prime and auxiliarycomponents using said IMU signal inputs.
 16. The system according toclaim 12, which includes: an inertial measurement unit (IMU) mounted onsaid machine and connected to said computer, said IMU sensing anattitude of said prime and auxiliary components relative to each otherand controlling said machine in response to output of said IMU.
 17. Thesystem of claim 12, which includes: an external computer; saidmachine-mounted computer being connected to said external computer; saidexternal computer being adapted to transfer field data input to saidguidance computer; and said machine-mounted computer being adapted totransfer field data output to said external computer.
 18. The system ofclaim 12, which includes: providing a switching circuit connected tosaid antennas and to said receiver; switching among said antennas withsaid switching circuit whereby respective antennas are selectivelyconnected to said receiver; providing GNSS-based ranging signal inputsto said computer based on relative positions of said antennas selectedby said switching circuit; and selecting said antennas with saidcomputer based on GNSS ranging signal quality characteristics.
 19. Thesystem of claim 12, which includes: a vehicle operating parameter sensoron said vehicle and connected to said machine-mounted computer; and saidcomputer correcting said guide path using said GNSS-defined positionsand vehicle operating parameters.
 20. The system of claim 12, whichincludes: providing a prime inertial measuring unit (IMU) on said primecomponent; providing an auxiliary IMU on said auxiliary component;providing output from said IMUs corresponding to roll (X), pitch (Y) andyaw (Z) movements of said prime and auxiliary components; inputting saidIMU output to said computer; and computing guide path corrections forsaid prime and auxiliary components using said IMU signal inputs. 21.The system of claim 12, which includes: an operating parameter sensorcomprising a camera mounted on said prime component and directed towardsa guide path.